1. Field of the Invention
The present invention relates to a gas laser apparatus, in particular to a gas laser apparatus for determining the composition ratio of a laser gas.
2. Description of the Related Art
In carbon dioxide gas laser oscillators, a laser gas circulating at high speed in a gas container is electrically discharged by a power supply for electrical discharge excitation, thereby generating laser light. A sheet metal cutting laser processing machine can cut a metal material, a resin material, or the like using laser light output from a carbon dioxide gas laser oscillator. The laser gas includes carbon dioxide gas, nitrogen gas, and helium gas as main components. The laser gas, which was produced by a gas manufacturer, has a previously designated composition ratio of carbon dioxide gas, nitrogen gas, and helium gas. Such a laser gas is supplied to the carbon gas laser oscillator through a laser gas piping system.
However, the composition ratio of actually produced laser gas is sometimes different from a designated composition ratio thereof. In addition, a laser gas having a composition ratio different from a designated one is sometimes erroneously connected to a carbon dioxide gas laser oscillator. In such a case, when the carbon dioxide gas laser oscillator is started, the oscillator stops and no laser light is output since electrical discharge impedance for the laser gas is different. As a result, the laser processing machine may not be able to cut sheet metal, a resin material, or the like.
Additionally, even when using a laser gas having an appropriate composition ratio, helium gas may leak outside from a laser gas piping system made of resin, since the helium gas included in the laser gas has small molecular weight. Additionally, even with the use of a laser gas piping system made of metal, when a pin hole is formed in the laser gas piping system, helium gas leaks from the pin hole. In such cases, the partial pressure of a helium gas component is reduced, which changes the composition ratio of the laser gas.
When the sheet metal cutting laser processing machine is relatively large, the distance from a laser gas source to the carbon dioxide gas laser oscillator may reach several tens of meters. Even in this case, due to the reason described above, the helium gas in the laser gas leaks, thereby reducing the partial pressure of the helium gas component. Furthermore, when helium gas leakage occurs in a state where laser gas remains in the laser gas piping system of a stopped carbon dioxide gas laser oscillator, the partial pressure of the helium gas component is similarly reduced.
As described above, when the laser gas in which the partial pressure of the helium gas component has been reduced is supplied to the carbon dioxide gas laser oscillator, an abnormality in the components of the laser gas is detected, as a result of which the oscillator itself is stopped. Alternatively, the power supply for electrical discharge excitation in the carbon dioxide gas laser oscillator detects the abnormality and stops, whereby no laser light is output.
A countermeasure for solving the problem described as above is to release the laser gas that contains the helium gas whose partial pressure has been reduced and that remains in the laser gas piping system, and also to supply a new laser gas to the carbon dioxide gas laser oscillator from the laser gas source.
Japanese Laid-open Patent Publication No. H4-80979 discloses a gas laser oscillator apparatus in which when helium gas leaks through a pin hole formed in a laser gas piping system, a predetermined amount of a laser gas in the laser gas piping system is released outside. Thereby, the composition ratio of the laser gas becomes normal, and therefore the carbon dioxide gas laser oscillator can be stably started.
In addition, Japanese Laid-open Patent Publication No. S61-22678 discloses a gas laser apparatus in which when electrical discharge starting voltage is high, the laser gas pressure of an electrically discharging unit in the oscillator is controlled so as to lower the electrical discharge starting voltage and changed to a laser gas pressure having favorable oscillation efficiency after starting electrical discharge.